It is known that in the handling of the filter-bag, after the same has been formed, it is important that the tag and its cotton thread are closely and firmly fitted on or adhered to the bag.
At present this is done by winding the thread around the bag and connecting it to the tag which is secured at one end of the bag. The fixing of the thread on the tag and on the bag is carried out by means of clips.
Another technique has been applied in bags formed from heat-sealable tapes. It is known that such tapes have on one face thereof a layer of heat-sealable thermoplastic material, which is partly diffused or spread into the interior of a web of filter paper. During the formation of the bags the tape is longitudinally folded into two halves so that the layer of thermoplastic material is arranged at the inside thereby allowing heat-sealing along the peripheral edges of the bag. In this type of bag the thread is replaced by a strip of heat-sealable thermoplastic material, which has one end thereof sealed between the peripheral heat-sealed edges of the bag and is sealed to the outside surface of the bag, at selected small areas.
It has been found that bags of this type, while being suitable for high productivity, have som essential drawbacks. First of all the cost of the strip affects in a remarkable manner the final confection, since such cost is remarkably greater than the cost of the conventional thread of natural fibers. Furthermore, definitely, the heat-sealable thermoplastic strip has the property to transfer to the infusion a strange disagreeable taste. Moreover the detachment between the strip and the bags is not always perfect and may cause the tearing of the bag walls and escape of product from the bag.